integration: make docker execute and ping timeouts CI-aware

The default docker execute timeout (10s) is the root cause of
"dockertest command timed out" errors across many integration tests
on CI. On congested GitHub Actions runners, docker exec latency
alone can consume 2-5 seconds of this budget before the command
even starts inside the container.

Replace the hardcoded 10s constant with a function that returns
20s on CI, doubling the budget for all container commands
(tailscale status, headscale CLI, curl, etc.).

Similarly, scale the default tailscale ping timeout from 200ms to
400ms on CI. This doubles the per-attempt budget and the docker
exec timeout for pings (from 200ms*5=1s to 400ms*5=2s), giving
more headroom for docker exec overhead.

Updates #3125

integration/tsic/tsic.go

@@ -39,13 +39,23 @@ import (
 
 const (
 	tsicHashLength       = 6
-	defaultPingTimeout   = 200 * time.Millisecond
 	defaultPingCount     = 5
 	dockerContextPath    = "../."
 	caCertRoot           = "/usr/local/share/ca-certificates"
 	dockerExecuteTimeout = 60 * time.Second
 )
 
+// defaultPingTimeoutVal returns the per-attempt timeout for tailscale ping.
+// On CI, the docker exec overhead is higher so the timeout is doubled,
+// which also doubles the docker exec timeout (timeout * count).
+func defaultPingTimeoutVal() time.Duration {
+	if util.IsCI() {
+		return 400 * time.Millisecond
+	}
+
+	return 200 * time.Millisecond
+}
+
 var (
 	errTailscalePingFailed             = errors.New("ping failed")
 	errTailscalePingNotDERP            = errors.New("ping not via DERP")
@@ -1348,7 +1358,7 @@ func WithPingUntilDirect(direct bool) PingOption {
 // TODO(kradalby): Make multiping, go routine magic.
 func (t *TailscaleInContainer) Ping(hostnameOrIP string, opts ...PingOption) error {
 	args := pingArgs{
-		timeout: defaultPingTimeout,
+		timeout: defaultPingTimeoutVal(),
 		count:   defaultPingCount,
 		direct:  true,
 	}